1. Field of the Invention
The present invention relates to an image processing apparatus and an image processing circuit, and more particularly, to an image processing apparatus and an image processing circuit applicable to different copying types of color copying machines.
2. Description of the Background Art
Conventionally, two types of color copying machines are known. The first type is a color copying machine of a four-cycle type including one photoreceptor drum and four developing units forming a toner image on the photoreceptor drum. The four developing units are respectively provided for four color toners of cyan (C), magenta (M), yellow (Y) and black (K). In the full color copying machine of the four-cycle type, the steps of forming an electrostatic latent image on the photoreceptor drum by the developing units and transferring the electrostatic latent image formed on the photoreceptor drum onto a sheet of paper are repeated four times in the order of cyan, magenta, yellow and black.
The second type is a color copying machine of a tandem type, in which photoreceptor drums are respectively provided corresponding to four developing units for cyan (C), magenta (M), yellow (Y) and black (K). In the tandem type color copying machine, electrostatic latent images are formed on the four photoreceptor drums almost at the same time, and the latent images formed on the respective photoreceptor drums are transferred when a sheet of paper makes contact with the four photoreceptor drums by turns.
Therefore, the tandem type copying machine has an advantage that an image forming speed is faster compared to the four-cycle type copying machine. However, the tandem type copying machine has a disadvantage such that the four receptor drums provided therein makes the machine more expensive compared to the four-cycle type color copying machine using one receptor drum. A user may desire a machine at a lower price even with low speed or a machine with high speed even at a higher price. Therefore, makers are required to provide various types of color copying machines in order to respond to the needs.
The color copying machines of the two types described above both include four developing units. Thus, the two types use the same data for forming electrostatic latent images in the respective developing units, i.e. the data for generating a laser emitting onto a receptor drum. Therefore, if a circuit from reading the original to outputting the data for the laser beam emission is designed separately for each type of the color copying machines, the enormous number of designing man-hours would be required, decreasing productivity.
Further, a unit price can generally be reduced as the number of items produced in quantity is increased, so that a common circuit may be used in terms of productivity and price.
However, the tandem type color copying machine generates the data for forming four electrostatic latent images of cyan, magenta, yellow and black to almost simultaneously write the data onto the respective photoreceptor drums, whereas the four-cycle type color copying machine generates the four data for cyan, magenta, yellow and black by turns to write the data in sequence. Thus, each type has different timing of data generation.
Generally, image data processing and a process of obtaining a characteristic such as a character or a photograph required for the data processing at a subsequent stage are performed in parallel. However, there is a problem that the process of obtaining a characteristic needs longer processing time compared to the image data processing performed in parallel therewith, since the process of obtaining the characteristic is performed based on a plurality of pixel data. The image data to be input into the subsequent stage must be delayed by the processing time period for obtaining a characteristic amount, in order to synchronously input the image data processed in the preceding stage and the characteristic amount processed in parallel therewith into the data processing in the subsequent stage. The number of memories in a circuit in which the data delay is required is defined by the number of data generated. Thus, the tandem type almost simultaneously generating four data would require four memories for four data in order to delay the four data, whereas the four-cycle type sequentially generating data would require only one memory for one data. However, a circuit used in common for the tandem type and the four-cycle type would have to include the number of memories needed for the type requiring a larger number of memories, resulting in a problem that unnecessary memories would be mounted for the type requiring a smaller number of memories, which increases the cost by that much.